As demands for higher IC operation speeds with smaller dimensions increases, it becomes a trend to integrate as many functions as possible into a single chip, i.e., system on chip, SOC, or to integrate several chips with different functions into a single package, such as, system in package, SIP. When integrating the functions of analog, memory, and logic functions into one single chip, there are some unsolved integration issues such as noise and voltage drop. R.O.C. Taiwan Patent publication No. 533,561 discloses a multi-chip stacked package, which comprises a substrate with an opening, at least a first chip, at least a second ship, at least a third chip, and an encapsulant. The opening penetrates the substrate. Moreover, the substrate has at least two layers of circuits inside for signal transmissions. The first chip is a flip chip attached to the first surface of the substrate above the opening through a plurality of flip-chip bumps for electrical connections to the substrate. The second chip is attached to the back surface of the first chip and is electrically connected to the substrate through a plurality of bonding wires. The third chip is flip-chip attached to the active surface of the first chip within the opening through a plurality of flip-chip bumps. Normally the third chip is SDRAM or another type of memory chip. An underfill material is disposed between the first chip and the third chip and between the first chip and the substrate. The encapsulant is formed on the top of the substrate to cover the bonding wires and the second chip. Since the third chip is electrically connected to the substrate through the first chip, the redistribution circuit design in the first chip becomes more complicated. In addition, since the signals of the third chip have to go through the first chip, noise will become an issue. To ensure the quality, the whole multi-chip package passes through burn-in. But another problem is that the third chip in the multi-chip package is not interchangeable when the multi-chip package had been burn-in and tested.